(Oh No) More Invaders from Space!
The name of the game is: (Oh No) More Invaders from Space, and it is by far the most fast-paced Space Invaders clone I’ve ever played. The graphics are pretty neat, too! The game has some additional elements such as power-ups, various weapons and apparently, from the site’s description, you have to protect cows from being kidnapped by the aliens (I haven’t got that far yet, but that should be interesting!).
Check out their website for the screenshots and download.